Sign up for google webmaster tools for www and non www. set the preferred url up in both accounts. wait... wait some more... and wait a long time more... voila, done.
A 301 will maybe do the trick on it's own, but could take longer.

Note that adblockers might block our captcha, and other functionality on BHW so if you don't see the captcha or see reduced functionality please disable adblockers to ensure full functionality, note we only allow relevant management verified ads on BHW.